fsck improvements

* fsck: Check if annex.numcopies is satisfied.
* fsck: Verify the sha1 of files when the SHA1 backend is used.
* fsck: Verify the size of files when the WORM backend is used.
* fsck: Allow specifying individual files to fsk if fscking everything
  is not desired.
* fsck: Fix bug, introduced in 0.04, in detection of unused data.

Locations.hs

@@ -13,6 +13,7 @@ module Locations (
 	annexLocation,
 	annexLocationRelative,
 	annexTmpLocation,
+	annexBadLocation,
 	annexDir,
 	annexObjectDir,
 
@@ -59,6 +60,10 @@ annexObjectDir r = annexDir r ++ "/objects"
 annexTmpLocation :: Git.Repo -> FilePath
 annexTmpLocation r = annexDir r ++ "/tmp/"
 
+{- .git-annex/bad is used for bad files found during fsck -}
+annexBadLocation :: Git.Repo -> FilePath
+annexBadLocation r = annexDir r ++ "/bad/"
+
 {- Converts a key into a filename fragment.
  -
  - Escape "/" in the key name, to keep a flat tree of files and avoid